1. Field of the Invention
The present invention relates to a two-armed transfer robot useful for semiconductor manufacturing equipment, liquid crystal display processing equipment and the like. More particularly, the present invention relates to a two-armed transfer robot for transferring workpieces between processing chambers under a vacuum.
2. Description of the Related Art
In general, transfer robots are used for semiconductor manufacturing equipment, liquid crystal display processing equipment and the like. The robot has at least one arm mechanism provided with a handling member. An object to be processed or workpiece such as a silicon wafer is placed on the handling member. The arm mechanism is capable of moving horizontally in a straight line as well as rotating in a horizontal plane. A plurality of processing chambers for performing various kinds of processing are arranged around a rotation axis of the robot. With the use of the transfer robot, the workpiece is suitably brought to and taken away from a selected one of the processing chambers.
For improving efficiency in the transferring operation, use has been made of the so-called two-armed transfer robot having two arm mechanisms. Each arm mechanism has a free end at which a handling member is mounted.
Conventionally, various kinds of two-armed transfer robots have been proposed. One example of such transfer robots is disclosed in JP-A-No. 7(1995)-142552 for example.
The conventional robot disclosed in the above document is shown in FIGS. 14-17 of the accompanying drawings.
Specifically, the illustrated conventional robot includes a stationary base frame 80, an inner frame 81 and a first arm 82. The inner frame is rotatable about a vertical axis O1 relative to the base frame 80, while the first arm is rotatable about a first axis P1 extending in parallel to the axis O1. The inner frame 81 is caused to rotate by a driving device fixed to the base frame 80, while the first arm 82 is caused to rotate by another driving device fixed to the inner frame 81.
Reference numeral 83 indicates a second arm which is rotatable relative to the first arm 82 about a second axis Q1 (see FIG. 15) extending in parallel to the first axis P1, while reference numeral 84A indicates a handling member which is rotatable relative to the arm 83 about a third axis R1 extending in parallel to the second axis Q1. Reference numeral 85 indicates a first rotation-transmitting member which is fixed to the inner frame 81 coaxially with the first axis P1, while reference numeral 86 indicates a second rotation-transmitting member which is fixed to the second arm 83 coaxially with the second axis Q1. Reference numeral 87 indicates a third rotation-transmitting member fixed to the first arm 82 coaxially with the second axis Q1, while reference numeral 88 indicates a fourth rotation-transmitting member fixed to the handling member 84 coaxially with the third axis R1.
A first connecting member 89 is provided between the first rotation-transmitting member 85 and the second rotation-transmitting member 86, while a second connecting member 90 is provided between the third rotation-transmitting member 87 and the fourth rotation-transmitting member 88. The distance S between the first and second axes is equal to the distance between the third and fourth axes. The radius ratio of the first rotation-transmitting member 85 to the second rotation-transmitting member 86 is 2 to 1. The radius ratio of the fourth rotation-transmitting member 88 to the third rotation-transmitting member 87 is also 2 to 1.
Chain sprockets or pulleys may be used for the first to fourth rotation-transmitting members 85-88. Correspondingly, the first and second connecting members 89, 90 may be chains or timing belts.
A first arm mechanism 91 is made up of the above-mentioned elements 82-90. A second arm mechanism 92, which is symmetrical to the first arm mechanism with respect to the X--X line, is supported for rotation about the second axis P2 extending in parallel to the axis O1.
Thus, the distance between the axis O1 and the first axis P1 is equal to that between the axis O1 and the second axis P2. The two-armed transfer robot is made up of the above elements 80-92.
The operations of the first and the second arm mechanisms 91, 92 are symmetrical with respect to the X--X line and substantially the same. Therefore, description will only be made to the operation of the first arm mechanism 91.
First, it is assumed that the inner frame 81 is kept stationary relative to the base frame 80, and that the first, second and third axes P1, Q1, R1 are initially located on a common straight line, as shown in FIG. 16. Starting from this state, the first arm 82 is rotated counterclockwise through an angle .theta. about the first axis P1.
During the above operation, the first rotation-transmitting member 85 is held stationary, while the second axis Q1 is moved counterclockwise around the first axis P1 through the angle .theta.. (Thus, the second axis Q1 is shifted from the initial position to a position Q11.) As a result, a Y1-side portion of the first connecting member 89 is wound around the first rotation-transmitting member 85, whereas a Y2-side portion of the same member is unwound from the first rotation-transmitting member 85.
Thus, as shown in FIG. 16, the first connecting member 89 is moved in a direction indicated by arrows a1 and a2. As a result, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q1.
As previously mentioned, the radius ratio of the first rotation-transmitting member 85 to the second rotation-transmitting member 86 is 2 to 1. Thus, when the first arm 82 is rotated counterclockwise about the first axis P1 through the angle .theta., the second rotation-transmitting member 86 is rotated clockwise about the second axis Q11 through an angle 2.theta..
At that time, since the second rotation-transmitting member 86 is fixed to the second arm 83, the second rotation-transmitting member 86 and the second arm 83 are rotated clockwise about the second axis Q1 through an angle 2.theta..
If the second arm 83 did not change its orientation relative to the first arm 82, the third axis would be brought to an R11 position shown by broken lines. In an actual operation, however, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q11 through an angle 2.theta.. Therefore, the third axis R11 is moved clockwise about the second axis Q11 through the same angle 2.theta., to be brought to the R12 position.
This means that, even after the first arm 82 is rotated counterclockwise about the first axis P1 through an angle .theta., the third axis R12 is still on the straight line extending through the first and the third axis P1 and R1.
When the second arm 83 is rotated clockwise about the second axis Q11 through an angle 2.theta., bringing the third axis R11 to the R12 position, a Y2-side portion of the second connecting member 90 is wound around the third rotation-transmitting member 87, whereas a Y1-side portion of the same member is unwound from the third rotation-transmitting member 87.
As a result, the second connecting member 90 will be shifted in a direction b1-b2 shown in FIG. 16. Thus, the fourth rotation-transmitting member 88 is rotated counterclockwise about the third axis R12.
When the second arm 83 is rotated clockwise about the second axis Q11 through an angle 2.theta. as described above, the fourth rotation-transmitting member 88 is rotated counterclockwise about the third axis R12 through an angle .theta. (the radius ratio of the fourth rotation-transmitting member 88 to the third rotation-transmitting member 87 is 2 to 1). As a result, a point C0 of the fourth rotation-transmitting member 88 is brought to a position C1 on the straight line passing through the first and the third axes P1, R12.
Upon rotation of the first arm 82 about the first axis P1 in the counterclockwise direction as described above, the first arm mechanism 91 is actuated in the X-direction. Accordingly, the handling member 84A is moved along the line passing through the first and the third axes P1, R1. During this operation, however, the handling member 84A does not change its attitude or orientation since it is fixed to the fourth rotation-transmitting member 88. (As stated above, the fourth rotation-transmitting member 88 maintains its initial orientation during the above operation.)
Likewise, the second arm mechanism 92 is actuated in the X-direction, with the second handling member 84B keeping its initial attitude along the line passing through the first and the third axes P2, R2.
The first and the second handling members 84A, 84B are arranged between the axes P1, P2 as viewed in the Y1-Y2 direction (FIG. 16). Further, the extremities of the handling members 84A, 84B are vertically spaced from each other. Thus, upon actuation of the arm mechanisms 91, 92, the handling members 84A, 84B can move along the X--X line passing through the axis O1 without interfering with each other.
When the inner frame 81 is rotated about the axis O1, the first and the second arm mechanisms 91, 92 are simultaneously rotated about the axis O1.
As shown in FIG. 17, a suitable number of processing chambers (six chambers, in the figure) are arranged around the axis O1 of the two-armed transfer robot. Workpieces are transferred by the robot to these chambers 71-76.
The conventional transfer robot has been found disadvantageous in the following respects.
First, as shown in FIGS. 14-16, the axis P1 of the first arm mechanism 91 and the axis P2 of the second arm mechanism 92 are spaced from each other, with the axis O1 of the inner frame 81 located therebetween. This arrangement renders the rotation radius of the inner frame 81 unfavorably large.
Accordingly, the bearings 93 provided around the inner frame 81 need to have an unfavorable large diameter. The magnetic fluid seal 94 for hermetic sealing suffers the same problem. With the use of such bearings and magnetic fluid seal, the overall size of the robot will be unfavorably large, so that the robot will become unduly expensive.
Another problem is that the driving devices for moving the handling members 84A, 84B are mounted on the inner frame 81. With such an arrangement, in operation, the driving devices are rotated together with the inner frame 81. However, in the conventional transfer robot, use is made of a cable extending from the base frame 80 for supplying the driving devices with electricity. Thus, in order to prevent breakage of the cable, it is necessary to stop the rotation of the inner frame 81 before it has been rotated too many times (more than 540.degree. for example) in the same direction.
For controlling the rotation of the inner frame 81, the user of the conventional robot may rely on an additional monitor and controlling unit for example. However, such devices make the transfer robot additionally expensive. More importantly, the additional devices merely serve to restrict the operational freedom of the transfer robot but cannot allow the user to operate the transfer robot freely.
Further, in the conventional robot, the first arm mechanism 91 and the second arm mechanism 92 are arranged to move together (simultaneously) around the first axis O1 upon rotation of the inner frame 81. Such an operation gives rise to the following inconvenience.
Referring to FIG. 17, it is assumed that a plurality of silicon wafers to be processed are initially stored in the chamber 72. For subjecting the silicon wafers to a predetermined processing, each of the stored silicon wafers needs to be transferred from the storing chamber 72 to one of the chambers 71 and 73-76. For that purpose, first, the first and second arm mechanisms 91, 92 are actuated, so that workpieces will be shifted onto the handling members 84A and 84B from the storing chamber 72. The silicon wafer placed on the handling member 84A (called "first wafer" hereinafter) may be carried into the chamber 73 (a target chamber), while the silicon wafer placed on the other handling member 84B (called "second wafer" hereinafter) may be carried into the chamber 71 (another target chamber).
For transferring the first wafer to the chamber 73, the inner frame 81 is caused to pivot clockwise (as seen in FIG. 17) through a certain angle (say, 45 degrees), so that the handling member 84A is brought into facing relation to the chamber 73. (The time needed for the inner frame 81 to perform the above pivoting movement will be called "time T1" hereinafter.) Then, the first arm mechanism 91 is actuated to shift the first wafer into the chamber 73. (The time needed for the first arm mechanism 91 to perform the shifting operation will be called "time T2.")
After the first wafer has been properly placed in the chamber 73, the inner frame 81 is caused to pivot counterclockwise through a certain angle (say, 90 degrees) to bring the handling member 84B into facing relation to the chamber 71. Then, the second arm mechanism 92 is actuated to shift the second wafer into the chamber 71. (The time needed for the inner frame 81 to rotate through a certain angle for moving the arm mechanisms from the chamber 73 to the storing chamber 72 will be called "time T3.")
In the conventional transfer robot, during the above operation, the second wafer is simply placed on the handling member 84B (i.e., without being subjected to any processing procedure) for the above-defined times T1, T2 and T3. This means that a certain length of idle time (the sum of the times T1, T2 and T3) has to unfavorably lapse before the processing for the second wafer can be started.
As can be seen, the above idle time will increase with the distance between the target chambers. In addition, the transferring operation may need to be performed many times a day (with respect to all of the target chambers 71 and 73-76). In that case, even if the idle time for each transfer operation is short, the total of the idle times may be unfavorably large.
In view of the problems described above, two-armed transfer robots capable of performing effective operations with less idle time have been conventionally sought for.